TiAl3 Layer Research Articles

Low-temperature formation of Ti2AlN during post-deposition annealing of reactive multilayer systems

Mn+1AXn-phase Ti2AlN thin-films were synthesized using reactive sputtering-based methods involving the deposition of single-layer TiAlN, and Ti/AlN and TiN/TiAl multilayers of various modulation periods at ambient temperature and subsequent annealing at elevated temperatures. Ex situ and in situ x-ray diffraction measurements were used to characterize the Ti2AlN formation temperature and phase fraction. During annealing, Ti/AlN multilayers yielded Ti2AlN at a significantly lower in situ temperature of 650 °C compared to TiN/TiAl multilayers or single-layer TiAlN (750 °C). The results suggest a reactive multilayer mechanism whereby distinct Ti and AlN layers react readily to release exothermic energy resulting in lower phase transition temperatures compared to TiN and TiAl layers or mixed TiAlN. With a modulation period of 5 nm, however, Ti/AlN multilayers yielded Ti2AlN at a higher temperature of 750 °C, indicating a disruption of the reactive multilayer mechanism due to a higher fraction of low-enthalpy interfacial TiAlN within the film.

Effect of Cr on microstructure and high temperature oxidation resistance of Ti-Al-Si composite coatings prepared by two-step hot-dipping + pre-oxidation method on Ti65 alloy

Titanium alloys have a thermal barrier temperature of 600℃, however, the preparation of Ti-Al-Si coating is one of the effective methods to improve the high temperature oxidation resistance of titanium alloys. Due to the preferential combination of Si and Ti, it is difficult to form a Ti-Al alloy phase layer with excellent oxidation resistance at high temperature. In order to solve this problem, the two-step hot-dipping + pre-oxidation method was creatively used to prepare Ti-Al-Si composite coatings, and a small amount of Cr was added to improve the high temperature oxidation resistance of the coatings. The phase structure of the coating was analyzed by XRD. The microstructure of the coating was characterized by SEM. EDS was used to analyze the content and distribution of elements in the coating. The results shown that the Cr-added Ti-Al-Si composite coatings were in the sequence of Ti3Al layer, TiAl layer, TiAl2 + Ti5Si3 layer, Ti(Al,Si,Cr)3 layer, L-(Al,Si) layer, and Al2O3 layer from the substrate. Cr segregated on the Ti(Al,Si,Cr)3 phase boundary, and promoted the selective oxidation of Al to form Al2O3. The dense and continuous Ti-Al binary intermetallic layer can prevent cracks from spreading to the substrate, which further improves the high temperature oxidation resistance.

Combustion-synthesised TiAl/NiAl layered intermetallic composite: synthesis, phase composition, and microstructure

ABSTRACT The joining of different intermetallics (e.g. NiAl, TiAl) is important for high-temperature applications. In this study, self-propagating high-temperature synthesis was used for simultaneous joining of (Ni+Al) and (Ti+Al) layered samples of the stoichiometric compositions. The main advantage of such joining by self-propagating high-temperature synthesis is that it could be done at ambient temperature without the use of a furnace. The applied load during combustion synthesis was used to improve the contact between the Ni-Al and Ti-Al layers. The obtained results demonstrate that TiAl/NiAl intermetallics were successfully joined together with a bonding interface of about 170 μm thickness. XRD analysis has shown that the joining area consists of NiAl, TiAl, Ti3Al, and NiTiAl2 phases. The SEM data analysis of the transition zone of NiAl-TiAl conjunction has revealed that the transition zone consists of several intermediate layers: a polycrystalline NiAl layer; an intermediate layer based on Ni-Al-Ti containing NiTiAl2 phase; a layer based on Ni-Al-Ti with mixed dendritic and eutectic regions; and a polycrystalline TiAl layer.The measured microhardness of the transition zone varies from 3200 up to 13,600 MPa with the maximum microhardness of 1355 ± 45 MPa corresponding to the layer identified as the NiTiAl2 phase.

Heterogeneous deformation-induced strengthening of extruded Tip/WE43 composites

Titanium (Ti) particles reinforced WE43 (Mg-4Y-2Nd-1Gd-0.5Zr) matrix composites (Tip/WE43) were prepared via ultrasonic-assisted stirring casting and following hot extrusion. Ti particles can refine the grains and promote the precipitation of the second phases in magnesium (Mg) matrix. Meanwhile, bimodal structures combining coarse deformed grains and recrystallization equiaxed grains were formed. The generation of heterogeneous interfaces promotes heterogeneous deformation-induced (HDI) strengthening. Extruded 3Tip/WE43 with a yield strength (YS) of 241 MPa, an ultimate tensile strength (UTS) of 283 MPa, and an elongation (EL) of 17.3%, respectively, possesses an excellent strength–ductility combination. The interfacial product of Ti/Mg was mainly composed Ti3Al layer with about 200 nm, which was conducive to interfacial bonding and stress transfer. The dislocation entanglements and stacking faults inside the Ti particles can promote the coordinated deformation between the Mg matrix and Ti particles. The rare-earth rich phases Ti2ZrAl, Mg41Nd5, and Mg24Y5 precipitated in the matrix can hinder dislocation movement by activating Orowan strengthening. The key factors of YS increment of the composites were considered to be HDI strengthening, fine grain strengthening, and thermal mismatch strengthening.

Underlying mechanisms of enhanced plasticity in Ti/Al laminates at elevated temperatures: A molecular dynamics study

The Ti/Al laminated metal components have attracted considerable attention due to their impressive strength and lightweight properties, positioning them as promising materials for aerospace and automotive applications. Although experimental evidence has highlighted their exceptional elongation and formability at elevated temperatures, there is still limited understanding of the underlying atomic-level mechanisms governing high-temperature plastic deformation, particularly with regards to the titanium aluminide (TiAl3) layer. This study utilized molecular dynamics (MD) simulations to investigate the tensile deformation of Ti/Al laminates, emphasizing the effects of temperature and TiAl3 layer thickness on atomic structural evolutions and mechanical properties. The MD simulations confirmed the decreases in the elastic modulus and peak stress at elevated temperatures, consistent with the experimental findings. The total dislocation length displayed an increasing trend with temperature, reaching a maximum at 600 K, before decreasing at 900 K due to amorphization. Moreover, the coordinated deformation among the Ti, Al and TiAl3 layers at elevated temperatures contributed to enhanced plasticity of the Ti/Al laminates. Furthermore, the TiAl3 layer thickness positively influenced the total dislocation length. However, increasing the layer thickness also leads to more high-strain bands in the TiAl3 layer, resulting in crack nucleation and decreased ductility of the Ti/Al laminate. This study provides valuable insights into the plastic deformation of Ti/Al laminates at elevated temperatures from the molecular dynamics perspective, benefitting further improvement in their plastic forming technique and engineering applications.

Effects of laser power on the microstructural evolution and mechanical performance in laser dissimilar welding of TC4 to SiCp/6092Al composite

In this study, an overlap configuration for Ti6Al4V alloy (TC4) and SiC particle reinforced aluminum matrix composites (AMC) was achieved by laser welding process. The influence of laser power on the microstructural evolution, intermetallic compounds formation and mechanical properties of TC4/AMC joints were investigated. The presence of reinforced phase SiC complicated the metallurgical reaction in the molten pool, resulting in the formation of intermetallic compounds, such as Al4C3, TiC, TiAl, and TiAl3. The influence of laser power was more pronounced on the penetration depth compared to its impact on the weld width. The thickness of TiAl intermetallic compounds at the TC4/AMC interface increased as the laser power was raised. Abundant dislocations existed surrounding the TiAl3 phase because of the different thermal-mechanical properties between Al matrix and TiAl3 phase. The tensile shear force of TC4/AMC joints can be considerably improved by reducing the thickness of the TiAl3 phase. The maximum tensile shear force of 1675.6 N for the TC4/AMC joint was obtained at a laser power of 1500 W when the thickness of the TiAl3 layer reached the lowest value of 7.1 μm. The research results have the potential to improve laser welding techniques for TC4/AMC hybrid structures and provide valuable guidance for the design of TC4/AMC welded joints in the future.

Interface property of dissimilar Ti–6Al–4V/AA1050 composite laminate made by non-equal channel lateral co-extrusion and heat treatment

The purpose of this paper is to examine the effect of processing parameters and subsequent heat treatments on the microstructures and bonding strengths of Ti–6Al–4V/AA1050 laminations formed via a non-equal channel lateral co-extrusion process. The microstructural evolution and growth mechanism in the diffusion layer were discussed further to optimize the bonding quality by appropriately adjusting process parameters. Scanning electron microscopes (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) were used to characterize interfacial diffusion layers. The shear test was used to determine the mechanical properties of the interfacial diffusion layer. The experimental results indicate that it is possible to co-extrusion Ti–6Al–4V/AA1050 compound profiles using non-equal channel lateral co-extrusion. Different heat treatment processes affect the thickness of the diffusion layer. When the temperature and time of heat treatment increase, the thickness of the reaction layers increases dramatically. Additionally, the shear strength of the Ti–6Al–4V/AA1050 composite interface is proportional to the diffusion layer thickness. It is observed that a medium interface thickness results in superior mechanical performance when compared to neither a greater nor a lesser interface thickness. Microstructural characterization of all heat treatments reveals that the only intermetallic compound observed in the diffusion layers is TiAl3. Due to the inter-diffusion of Ti and Al atoms, the TiAl3 layer grows primarily at AA1050/TiAl3 interfaces.

Micro-/nano-scale interface structure and mechanical characteristics of the Al/Ti composite bar produced by a novel continuously-extruded technique

In this work, a novel extrusion die for embedding the continuous Ti wire into the aluminum alloy is developed, and the extruded composite bar is obtained. The multi-scale interface structure, elemental diffusion, and mechanical characteristics are investigated by different material characterization methods. The three-dimensional (3D) amorphous regions are produced on the well-bonded Al/Ti interface. The formation of a nanocrystalline Al layer is accompanied by the precipitation of Mg-/Si-enriched clusters. With an increase in the annealing time, the average grain size of TiAl3 increases, while the dislocation density of the TiAl3 layer decreases. A nanoscale TiAl3 monolayer is exhibited between the Al/TiAl3 and Kirkendall interfaces, whereas two types of nanoscale TiAl3 grains are detected on the Ti/TiAl3 interface. The Si-enriched clusters are aggregated at the Ti/TiAl3 interface, generating a nanoscale layer. Local inhibition behaviors of large-sized Mg-enriched clusters on the growth of TiAl3 are observed at the Al/TiAl3 interface after annealing for 48 h. Not only are massive misfit dislocations and distorted lattices detected on the 3D interface, but also locally ordered transition zones are noticed. The extruded composite bar exhibits a superior strength-ductility balance, which provides a new strategy for the development of aluminum profiles.

Formability improvement of hot-pressed Ti/Al laminated sheet by TiAl3 layer growth and crack healing during deformation

Ti/Al laminated sheets were prepared by hot pressing pure Ti and Al foils at 630 °C/20 MPa for different times. The thickness of TiAl3 layers increased, and the elongation of the Ti/Al laminated sheet decreased with the hot-pressing time, where the 15 min-hot-pressed sheets showed the most extensive elongation (135% at 600 °C). The crack initiation and propagation behavior of the 15 min-hot-pressed sheets were investigated by the tensile test with different strains. When the testing temperature was between room temperature (RT) and 400 °C, the cracks in TiAl3 layers were parallel to each other and perpendicular to the tensile direction. The size and amounts of cracks increased with the strain. At 600 °C, the parallel cracks appeared after 70% deformation, while at 100% strain, the TiAl3 layer thickness increased significantly, accompanied by many disordered and discontinuous cracks. The 15 mins-hot-pressed sheet shows excellent gas bulging formability, where the height to radius ratio reached 0.9. The improved sheet formability is because the cracks were filled and healed by the newly formed TiAl3 phase during deformation at 600 °C. The TiAl3 layer, therefore, was maintained for a longer time before rupturing, which greatly improved the coordination deformation ability of various layers.

Effect of Ti particles on microstructure and mechanical properties of TiP/AZ91 composites

Ti particles (5 wt%) reinforced AZ91 Mg matrix composites (TiP/AZ91 composites) were prepared by powder metallurgy. As a result, the strength and ductility of TiP/AZ91 composites were improved compared with AZ91 alloy. The ultimate tensile stress (UTS) increased significantly from 163 MPa to 221 MPa, and the elongation increased from 3.5% to 10.9%. The YS and hardness decreased due to the slightly coarser grain size. The microstructural results showed that Ti particles were uniformly dispersed in the Mg matrix and the content of Mg17Al12 was reduced, indicating that Ti particles can inhibit the precipitation of the second phase. The interface between Ti particle and Mg matrix showed that the Al3Ti layer was formed at the edge of the Ti particles. EBSD was used to analyze the twins and dislocations at different tensile strains. During the tensile deformation at room temperature, many tensile twins and dislocations formed in the TiP/AZ91 composites. The tensile twins and dislocations could coordinate plastic deformation, thus improving the elongation of the TiP/AZ91 composites.

Effect of hot-pressing temperature on microstructure and the improvement of residual Al on tensile ductility of Ti/Al3Ti heterogeneous structure

Ti/Al3Ti Heterogeneous Structures (HS) with different fractions of residual Al were fabricated at hot-pressing temperatures from 580 °C to 650 °C. The grain boundary distribution and Kernel Average Misorientation (KAM) were characterized by EBSD technique. The varied tensile properties and failure modes were specified, and the local strain evolution was analyzed by DIC. Results show that the distribution of grain boundary, the thickness of individual layers, and mechanical properties were significantly affected by hot-pressing temperature. The elongation of Ti/Al3Ti/Al HS was 64.2%–228.5% higher than that of Ti/Al3Ti HS, which was attributed to stabilized plastic flow and the regulating effect of residual Al. The improvement mechanisms of residual Al on tensile plasticity were found that normal strain was delocalized by promoting strain flow, and shear strain was stabilized by hindering effects. In addition, the tensile strength and work-hardening capability were enhanced by the grain refinement of TC4 layer. The failure mechanism, from HS650 to HS600, is found to transform from brittle fracture determined by normal strain into ductile shearing fracture governed by normal strain and shearing strain. The fracture micromorphology revealed that a mixed model of transgranular and intergranular was presented in the Al3Ti layers. Dimples were distributed in TC4 layers, and tearing ridges were overspread in Al layers. The current views on localized characterizations perhaps provide more complete insights toward the technics-properties design of Ti/Al3Ti HS.

Effect of bias voltage on microstructure, mechanical and tribological properties of TiAlN coatings

TiAlN multilayer coatings composed of TiAl and TiAlN layers were deposited on ZL109 alloys using filtered cathodic vacuum arc (FCVA) technology. The effect of bias voltage on the microstructure and properties of the coating was systematically studied. The results show that the coating exhibits a multi-phase structure dominated by TiAlN phase. As the bias voltage increases, the orientation of TiAlN changes from (200) plane to (111) plane due to the increase of atomic mobility and lattice distortion. The hardness, elastic modulus and adhesion of the coating show the same trend of change, that is, first increase and then decrease. When the bias voltage is 75 V, the coating exhibits the highest hardness (~30.3 GPa), elastic modulus (~229.1 GPa), adhesion (HF 2) and the lowest wear rate (~4.44×10−5 mm3/(N·m)). Compared with bare ZL109 alloy, the mechanical and tribological properties of TiAlN coated alloy surface can effectively be improved.

High-Temperature Oxidation Behaviour of a TiAl-Based Alloy Subjected to Aluminium Hot-Dipping

In this research the oxidation resistance at high temperature of a TiAl-based alloy has been improved by hot-dipping the alloy in molten aluminium and by performing an interdiffusion process. After selecting the best process parameters, a compact TiAl3 coating characterized by an almost constant thickness was formed on the surface. Isothermal oxidation tests, carried out at 900, 950 and 1000 °C, showed that the coated alloy is able to form a continuous and thin alumina layer that is very protective. Microstructural investigations highlighted that, above 900 °C, long residence times at high temperature determine the diffusion through the TiAl3 layer of Cr that favours migration toward the outer surface of Al and thus the formation of a self-healing alumina layer.Graphical

Surface protection of a V-4Cr-4Ti alloy through a multilayered TiAl/TiAlN composite coating

The vanadium alloys are attractive structural materials for applications in Generation IV reactors and fusion reactors. Surface protections of the alloy are required due to its high affinity to H, O etc. impurity atoms. The previous coating designs on the vanadium alloys have been focused on monolithic coatings and may have low coating-substrate bonding strengths. The TiAlN-based composite coatings which show remarkable surface protection effects, are yet to be applied to the vanadium alloy substrates. In the current work, a TiAl/TiAlN composite coating with intermediate TiAl layers was deposited on a V-4Cr-4Ti alloy substrate using the filtered-cathodic vacuum-arc-deposition (FCVAD) method. The coating with a total thickness of ∼18 μm was compact and free of any voids or inclusions. A high adherence strength of ∼82 N was measured for the coating. The ultrafine equi-axed γ-TiAl grains in the TiAl layer, and the columnar grains in the TiAlN layer which are composed of a mixture of TiN/AlN/Ti3AlN phases were characterized in detail with the transmission electron microscopy (TEM). The surface hardness and surface roughness were significantly improved for the coating compared with the substrate. The electrochemical corrosion results also show that the composite coating offers improved corrosion resistance against aqueous corrosion at room temperature.

Microstructure and high-temperature oxidation behaviors of surface layer on TA2 pure titanium by boriding and aluminizing two-steps method

The surface layer on pure TA2 titanium was manufactured using boriding and aluminizing two-step methods. High-temperature oxidation experiments were carried out at 600 °C, 700 °C, and 800 °C for 100 h. Microstructure characterization of the surface layer was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). After 1050°C-4 h boriding and 1050°C-4 h aluminizing, the composite layer from the surface to the matrix consists of a TiB2 layer, TiB whisker + Al3Ti layer, Al3Ti layer, and diffusion layer. The Al3Ti layer could effectively protect the matrix, and thus, the borided and aluminized pure titanium shows excellent high-temperature oxidation resistance.

Diffusion bonding of implantable Al2O3/Ti-13Nb-13Zr joints: Interfacial microstructure and mechanical properties

In this study, implantable Al2O3/Ti-13Nb-13Zr (TNZ) alloy joints were achieved by diffusion bonding. The effects of bonding temperature and holding time on interfacial microstructure and mechanical properties were investigated. The interfacial microstructures of the joints bonded at various temperatures and holding time were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The typical microstructure of the Al2O3/TNZ joint, which was obtained at 1175 °C for 60 min under a pressure of 3 MPa, was Al2O3 ceramic/TiAl layer + TiO2 + Nb2O5 + AlNb2/continuous Ti3Al layer/acicular Ti3Al + Ti (s,s)/TNZ substrate. The presence of Ti element mainly contributed to the metallurgical bonding between TNZ and Al2O3 ceramic. Nb reacted with Al2O3 ceramic forming Nb2O5 and AlNb2 phases which played important roles in interfacial bonding. With the increase of bonding temperature or holding time, TiAl layer and Ti3Al layer thickened gradually while the number of Nb2O5 and AlNb2 first increased and then decreased. This corresponded to the change of average shear strength of these joints, which initially rose and then declined. The maximum of average shear strength reached 52.0 MPa when joints bonded at 1175 °C for 60 min under a pressure of 3 MPa, and the bonded joints mainly fractured at Al2O3 ceramic.

Laser-induced combustion joining of Cf/Al composites and TC4 alloy

The Cf/Al composites were joined to the TC4 alloy via the laser-induced combustion joining method. The exothermic reaction of the interlayer provided the required energy for the joining process. By combining the theoretical calculation and experiment, the chemical composition of the Ni–Al–Zr interlayer was designed. The microstructure and mechanical properties of the joint were investigated. The results show that the addition of Zr slightly weakened the combustion reaction of exothermic interlayer but played a key role in the successful joining. Ni–Al–Zr interlayer reacted with substrates, forming a TiAl3 layer adjacent to TC4 alloy and NiAl3, Ni2Al3 layers adjacent to the Cf/Al composites. Zr content dominated the microstructure and shear strength of the joint. When the Zr content was 5 wt.% under the joining pressure of 2 MPa, the joint had a maximum shear strength of 19.8 MPa.

Microstructure, mechanical and tribological properties of multilayer TiAl/TiAlN coatings on Al alloys by FCVA technology

In order to improve the surface properties of Al alloy, TiAlN ceramic coatings composed of alternating TiAl layer and TiAlN layer were prepared by FCVA technology. The influence of N 2 flow rate on the microstructure, mechanical and tribological performance of multilayer TiAlN coatings was systematically studied. The results showed that the coating exhibited a multi-phase structure with mainly fcc TiAlN phase and a small amount of TiN and AlN phases. As the N 2 flow rate increased from 50 to 80 sccm, the preferred orientation varied from TiAlN (220) plane to (111) plane due to lattice distortion. The hardness and elastic modulus of multilayer TiAlN coatings first increased and then decreased with the increase of N 2 flow rate. However, the average friction coefficient and wear rate of multilayer TiAlN coatings exhibited an opposite trend to the hardness, H/E and H 3 /E 2 values. The adhesion gradually decreased from 27.3 to 14.9 N due to the continuous increase of the compressive stress in the coating with the increase of N 2 flow rate. When the N 2 flow rate was 70 sccm, the coating showed the lowest average friction coefficient and wear rate, which was attributed to the highest hardness and the best resistance to cracking and plastic deformation.

Based on Genetic Algorithm to Analyze the Anti-Penetration Properties and Optimize the Structure of Ti-Al3Ti-Al Laminated Composites

A coupled finite-element genetic algorithm technique was used to optimize the arrangement order and layer thickness ratios of Ti-Al3Ti-Al laminated composites. Moreover, the damage evolution, energy conversion, and stress distribution of TC4-Al3Ti-Al laminated composites under impact were analyzed. The results showed that TC4-Al3Ti-Al laminated composites with a layer thickness ratio of 3:14:4 have optimum anti-penetration properties; the projectile kinetic energy is mainly converted into the internal energy of the bullet target system; during the penetration process of TC4-Al3Ti-Al targets, the TC4 layer is shear failure, the Al layer is a petal-like failure, the failure mode of Al3Ti layer is fragmentation; with the number of layer increases, the anti-penetration properties of TC4-Al3Ti-Al targets are gradually increasing. However, when the number of layers is more than 30 layers, the number of layers has little effect on the anti-penetration performance of these composites.

Wear and corrosion properties of a B–Al composite layer on pure titanium

A boriding and aluminizing two-step method was used to fabricate a B–Al composite layer on the surface of pure titanium. The composite layer was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoindentation, wear tests, and electrochemical experiments. For comparison, single boriding and single aluminizing treatments were performed on pure titanium. The results show that the surface morphology characteristics from the single boriding and single aluminizing treatments were transferred to the composite sample. The XRD pattern reveals that the B–Al composite layer also has XRD peaks of Al3Ti+TiB2+TiB. The SEM results revealed that the B–Al composite layer is composed of an outermost TiB2 layer, a TiB+Al3Ti sublayer, an Al3Ti layer, and an internal diffusion layer. The corrosion resistance of the composite sample is slightly better than that of the matrix, and the hardness is approximately 3 times higher than that of the matrix. The wear type is mainly abrasive wear, and the wear resistance is improved; with increasing temperature, the wear on the surface of the sample is intensified, and the wear resistance is reduced.